U.S. patent number 7,973,466 [Application Number 11/086,674] was granted by the patent office on 2011-07-05 for organic electroluminescent display device with light-shielding means and method of fabricating the same.
This patent grant is currently assigned to LG Display Co., Ltd.. Invention is credited to Hoon-Ju Chung, Yong-Min Ha, Byeong-Koo Kim, Du-Hwan Oh.
United States Patent |
7,973,466 |
Oh , et al. |
July 5, 2011 |
Organic electroluminescent display device with light-shielding
means and method of fabricating the same
Abstract
An organic electroluminescent display device includes: a
substrate having a pixel region and a non-pixel region surrounding
the pixel region; a first electrode on the substrate in the pixel
region; an organic luminescent layer on the first electrode; a
second electrode on the organic luminescent layer; and a
light-shielding means corresponding to the non-pixel region.
Inventors: |
Oh; Du-Hwan (Cheong,
KR), Chung; Hoon-Ju (Pyeongtaek, KR), Kim;
Byeong-Koo (Gumi, KR), Ha; Yong-Min (Gumi,
KR) |
Assignee: |
LG Display Co., Ltd. (Seoul,
KR)
|
Family
ID: |
34988991 |
Appl.
No.: |
11/086,674 |
Filed: |
March 23, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050212447 A1 |
Sep 29, 2005 |
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Foreign Application Priority Data
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Mar 23, 2004 [KR] |
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10-2004-0019734 |
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Current U.S.
Class: |
313/501; 313/505;
313/512; 313/500; 313/503; 445/25; 445/24 |
Current CPC
Class: |
H01L
27/3283 (20130101); H01L 27/3272 (20130101); H01L
51/5284 (20130101); H01L 27/3246 (20130101) |
Current International
Class: |
H01L
51/50 (20060101); H01L 51/56 (20060101); H01L
51/52 (20060101) |
Field of
Search: |
;313/500-512 ;315/169.3
;257/72 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Santiago; Mariceli
Attorney, Agent or Firm: McKenna Long & Aldridge LLP
Claims
What is claimed is:
1. An organic electroluminescent display device, comprising: a
substrate having a pixel region and a non-pixel region surrounding
the pixel region; a thin film transistor on the substrate and
including a semiconductor layer, a gate electrode, a source
electrode and a drain electrode; a storage capacitor connected to
the source electrode and including a first capacitor electrode and
a second capacitor electrode, wherein the first capacitor electrode
is formed of a same material and on a same layer as the
semiconductor layer, and the second capacitor electrode is formed
of a same material and on a same layer as the gate electrode,
wherein the second capacitor electrode is connected to the source
electrode; a first electrode on the substrate in the pixel region
and connected to the drain electrode; an organic luminescent layer
on the first electrode; a second electrode on the organic
luminescent layer; a light-shielding means corresponding to the
non-pixel region; and an encapsulation substrate formed of a
transparent material and configured to face and be spaced apart
from the second electrode, wherein the light-shielding means
includes a black matrix on an inner surface of the encapsulation
substrate, wherein the light-shielding means includes a material
having a transmittance lower than about 10% for a visible ray,
wherein the first electrode, the organic luminescent layer and the
second electrode form an organic electroluminescent diode, and
light emitted from the organic electroluminescent diode directly
goes onto the encapsulation substrate without the presence of a
color conversion element, wherein the light-shielding means is
spaced apart from the second electrode, and wherein the
light-shielding means covers the storage capacitor.
2. The device according to claim 1, wherein the visible ray has a
wavelength within a range of about 380 nm to about 780 nm.
3. The device according to claim 1, further comprising a switching
element connected to the first electrode.
4. The device according to claim 3, wherein the first electrode is
separately formed in the pixel region and the second electrode is
formed to cover an entire surface of the substrate.
5. The device according to claim 1, wherein the second electrode is
transparent.
6. A method of fabricating an organic electroluminescent display
device, comprising: providing a substrate having a pixel region and
a non-pixel region surrounding the pixel region; forming a thin
film transistor on the substrate and including a semiconductor
layer, a gate electrode, a source electrode and a drain electrode;
forming a storage capacitor connected to the source electrode and
including a first capacitor electrode and a second capacitor
electrode, wherein the first capacitor electrode is formed of a
same material and on a same layer as the semiconductor layer, and
the second capacitor electrode is formed of a same material and on
a same layer as the gate electrode, wherein the second capacitor
electrode is connected to the source electrode; forming a first
electrode on the substrate in the pixel region and connected to the
drain electrode; forming an organic luminescent layer on the first
electrode; forming a second electrode on the organic luminescent
layer; and forming a light-shielding means corresponding to the
non-pixel region; and disposing an encapsulation substrate formed
of a transparent material to face and be spaced apart from the
second electrode, wherein the forming the light-shielding means
includes forming a black matrix on an inner surface of the
encapsulation substrate, wherein the light-shielding means is
formed of a material having a transmittance lower than about 10%
for a visible ray, wherein the first electrode, the organic
luminescent layer and the second electrode form an organic
electroluminescent diode, and light emitted from the organic
electroluminescent diode directly goes onto the encapsulation
substrate without the presence of a color conversion element,
wherein the light-shielding means is spaced apart from the second
electrode, and wherein the light-shielding means covers the storage
capacitor.
Description
The present application claims the benefit of Korean Patent
Application No. 2004-0019734 filed in Korea on Mar. 23, 2004, which
is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display device, and more
particularly, to an organic electroluminescent (EL) display device
and a method of fabricating the same.
2. Discussion of the Related Art
Among flat panel displays (FPDs), organic electroluminescent (EL)
devices have been of particular interest in research and
development because they are light-emitting type displays having a
wide viewing angle as well as a high contrast ratio in comparison
to liquid crystal display (LCD) devices. Organic EL devices are
lightweight and small, as compared to other types of display
devices, because they do not need a backlight. Organic EL devices
have other desirable characteristics, such as low power
consumption, superior brightness and fast response time. When
driving the organic EL devices, only a low direct current (DC)
voltage is required. Moreover, a fast response time can be
obtained. Unlike LCD devices, organic EL devices are entirely
formed in a solid phase arrangement. Thus, organic EL devices are
sufficiently strong to withstand external impacts and also have a
greater operational temperature range. Moreover, organic EL devices
are fabricated in a relatively simple process involving few
processing steps. Thus, it is much cheaper to produce an organic EL
device in comparison to an LCD device or a plasma display panel
(PDP). In particular, only deposition and encapsulation processes
are necessary for manufacturing organic EL devices.
There are two types of organic EL display devices: passive matrix
type and active matrix type. While both the passive matrix organic
EL display device and the active matrix organic EL display device
have simple structures and are formed by a simple fabricating
process, the passive matrix organic EL display device requires a
relatively high amount of power to operate. In addition, the
display size of a passive matrix organic EL display device is
limited by its structure. Furthermore, as the number of conductive
lines increases, the aperture ratio of a passive matrix organic EL
display device decreases. In contrast, active matrix organic EL
display devices are highly efficient and can produce a high-quality
image for a large display with a relatively low power.
FIG. 1 is a schematic circuit diagram of an organic
electroluminescent display device according to the related art. In
FIG. 1, a switching thin film transistor (TFT) "T.sub.S" as an
addressing element is connected to a gate line 22 and a data line
40. A storage capacitor "C.sub.ST" is connected to the switching
TFT "T.sub.S," and a driving TFT "T.sub.D" as a current source
element is connected to the switching TFT "T.sub.S" and the storage
capacitor "C.sub.ST." The driving TFT "T.sub.D" is also connected
to a power line 26 and an organic electroluminescent (EL) diode
"E." The switching TFT "T.sub.S" adjusts a voltage of a terminal of
the driving TFT "T.sub.D" and the storage capacitor "C.sub.ST"
stores charges for the voltage of the terminal of the driving TFT
"T.sub.D."
FIG. 2 is a schematic plane view showing an organic
electroluminescent display device according to the related art. In
FIG. 2, a gate line 22 is formed along a first direction on a
substrate, and a data line 40 is formed along a second direction
intersected with the gate line 22, thereby defining a pixel region
"P." A power line 26 also is formed along the second direction and
spaced apart from the data line 40. A gate insulating layer (not
shown) is interposed between the gate line 22 and the data line
40.
In addition, a switching thin film transistor (TFT) "T.sub.S" is
connected to the gate line 22 and the data line 40. A driving TFT
"T.sub.D" is connected to the switching TFT "T.sub.S" and the power
line 26, and a storage capacitor "C.sub.ST" is connected to the
driving TFT "T.sub.D." A first electrode 46 is connected to driving
TFT "T.sub.D," and an organic luminescent layer (not shown) and a
second electrode (not shown) are sequentially formed on the first
electrode 46.
FIGS. 3A to 3I are schematic cross-sectional views, which is taken
along a line III-III of FIG. 2, showing a fabricating process of an
organic electroluminescent display device according to the related
art.
In FIG. 3A, a buffer layer 12 is formed on a substrate 10. A
semiconductor layer 14 of polycrystalline silicon and a first
capacitor electrode 16 are formed on the buffer layer 12 through a
first mask process.
In FIG. 3B, a first photoresist (PR) pattern 15 is formed on the
semiconductor pattern 14 through a second mask process. Next, the
first capacitor electrode 16 is doped with impurities using the
first PR pattern as a doping mask.
In FIG. 3C, a gate insulating layer 18 is formed on the
semiconductor pattern 14 and the first capacitor electrode 16.
Next, a gate electrode 20 and a second capacitor electrode 24 are
formed on the gate insulating layer 18 through a third mask
process. The gate electrode 20 and the second capacitor electrode
24 correspond to a central portion of the semiconductor pattern 14
and the first capacitor electrode 16, respectively. Next, the
semiconductor layer 14 is doped with impurities using the gate
electrode 20 as a doping mask. Since the gate electrode 14 shields
the central portion of the semiconductor layer 14, side portions of
the semiconductor layer 14 are doped with impurities and the
central portion of the semiconductor layer 14 remains intrinsic.
After the doping step, the semiconductor layer 14 includes an
active region "Sa" corresponding to the gate electrode 20, a source
region "Sb" and a drain region "Sc."
In FIG. 3D, after an activation step for the doped impurities, an
interlayer insulating layer 28 is formed on the gate electrode 20
and the second capacitor electrode 24. Next, the interlayer
insulating layer 28 and the gate insulating layer 18 are etched
through a fourth mask process. Accordingly, a first contact hole 30
exposing the drain region "Sc" and a second contact hole 32
exposing the source region "Sb" are formed in the interlayer
insulating layer 28 and the gate insulating layer 18, and a third
contact hole 34 exposing the second capacitor electrode 24 is
formed in the interlayer insulating layer 28.
In FIG. 3E, a drain electrode 36 and a source electrode 38 are
formed on the interlayer insulating layer 28. The drain electrode
36 is connected to the drain region "Sc" through the first contact
hole 30. In addition, the source electrode 38 is connected to the
source region "Sb" through the second contact hole 32 and is
connected to the second capacitor electrode 24 through the third
contact hole 34.
In FIG. 3F, a passivation layer 42 is formed on the drain electrode
36 and the source electrode 38. Next, the passivation layer 42 is
etched through a sixth mask process to form a drain contact hole 44
exposing the drain electrode 36.
In FIG. 3G, a first electrode 46 is formed on the passivation layer
42 through a seventh mask process. The first electrode 46 is
connected to the drain electrode 36 through the drain contact hole
44. Although not shown in FIG. 3G, the first electrode 46 of one
pixel region is separated from an adjacent first electrode in
another pixel region.
In FIG. 3H, a bank layer 48 is formed on the passivation layer 42
through an eighth mask process. The bank layer 48 covers edge
portions of the first electrode 46.
In FIG. 3I, an organic luminescent layer 50 and a second electrode
52 are sequentially formed on the first electrode 46 and the bank
layer 48.
FIG. 4 is a schematic cross-sectional view of an organic
electroluminescent display device according to the related art. In
FIG. 4, an organic electroluminescent (EL) diode "E" is formed on
an array layer "AL." The organic EL diode "E" includes a first
electrode 46, an organic luminescent layer 50 and a second
electrode 52, and the array layer "AL" includes a thin film
transistor (TFT) "T," a storage capacitor "C.sub.ST" and a
plurality of signal lines (not shown). A protection layer 54 is
formed on the organic EL diode "E" to protect the second electrode
52 of the organic EL diode "E."
The TFT "T," the storage capacitor "C.sub.ST" and a plurality of
signal lines (not shown) of the array layer "AL" include metallic
materials. In addition, when the second electrode 52 functions as a
cathode, a metallic material such as nickel (Ni) having a
relatively low work function is used for the second electrode 52.
Accordingly, ambient light may reflect from layer including the
metallic materials during the organic EL display device is driven,
and reflected light deteriorates display quality of the organic EL
display device such as a contrast ratio. For example, when the
organic EL display device has a top emission type, ambient light
reflects from the second electrode 52 and a first reflected light
"R1" is emitted toward users. Similarly, the ambient light reflects
from the array layer "AL" such as the TFT "T" and the storage
capacitor "C.sub.ST," and second and third reflected light "R2" and
"R3" are emitted toward users. The first, second and third
reflected light "R1," "R2" and "R3" may increase brightness of a
black image, thereby deteriorating a contrast ratio of the organic
EL display device.
As referring again to FIG. 3I, a cleaning step using ultra violet
(UV) ray is performed to remove organic particles from the first
electrode 46 before the organic luminescent layer 50 on the first
electrode 46. However, the UV ray may penetrate the bank layer 48,
the passivation layer 42 and the interlayer insulating layer 28 to
be irradiated onto the semiconductor layer 14. Accordingly, the
semiconductor layer 14 may be deteriorated by the UV ray and the
deterioration of the semiconductor layer 14 may cause degradation
in characteristics of the TFT. For example, a threshold voltage of
the TFT may be changed and a display quality of the organic EL
display device is deteriorated.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an organic
electroluminescent display device and a method of fabricating the
same that substantially obviate one or more of the problems due to
limitations and disadvantages of the related art.
An object of the present invention is to provide an organic
electroluminescent display device having an improved display
quality by preventing reduction of contrast ratio.
Another object of the present invention is to provide an organic
electroluminescent display device having an improved display
quality by preventing deterioration in characteristic of a thin
film transistor.
Additional features and advantages of the invention will be set
forth in the description which follows, and in part will be
apparent from the description, or may be learned by practice of the
invention. The objectives and other advantages of the invention
will be realized and attained by the structure particularly pointed
out in the written description and claims hereof as well as the
appended drawings.
To achieve these and other advantages and in accordance with the
purpose of the present invention, as embodied and broadly described
herein, an organic electroluminescent display device includes: a
substrate having a pixel region and a non-pixel region surrounding
the pixel region; a first electrode on the substrate in the pixel
region; an organic luminescent layer on the first electrode; a
second electrode on the organic luminescent layer; and a
light-shielding means corresponding to the non-pixel region.
In another aspect, a method of fabricating an organic
electroluminescent display device includes: providing a substrate
having a pixel region and a non-pixel region surrounding the pixel
region; forming a first electrode on the substrate in the pixel
region; forming an organic luminescent layer on the first
electrode; forming a second electrode on the organic luminescent
layer; and forming a light-shielding means corresponding to the
non-pixel region.
It is to be understood that both the foregoing general description
and the following detailed description are exemplary and
explanatory and are intended to provide further explanation of the
invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are included to provide a further
understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and together with the description serve to explain
the principles of the invention. In the drawings:
FIG. 1 is a schematic circuit diagram of an organic
electroluminescent display device according to the related art;
FIG. 2 is a schematic plane view showing an organic
electroluminescent display device according to the related art;
FIGS. 3A to 3I are schematic cross-sectional views, which is taken
along a line III-III of FIG. 2, showing a fabricating process of an
organic electroluminescent display device according to the related
art;
FIG. 4 is a schematic cross-sectional view of an organic
electroluminescent display device according to the related art;
FIG. 5 is a schematic cross-sectional view showing a passive matrix
organic electroluminescent display device according to an exemplary
embodiment of the present invention;
FIG. 6 is a schematic cross-sectional view showing an active matrix
organic electroluminescent display device according to another
exemplary embodiment of the present invention;
FIGS. 7A to 7C are schematic cross-sectional views showing a
fabricating process of an organic electroluminescent display device
of FIG. 6;
FIG. 8 is a schematic cross-sectional view showing one pixel region
of an active matrix organic electroluminescent display device
according to another exemplary embodiment of the present
invention;
FIG. 9 is schematic cross-sectional view showing a whole active
matrix organic electroluminescent display device according to
another exemplary embodiment of the present invention;
FIG. 10 is a schematic cross-sectional view showing an organic
electroluminescent display device according to another embodiment
of the present invention; and
FIGS. 11A and 11B are schematic cross-sectional views showing a
fabricating process of an organic electroluminescent (EL) display
device according to another exemplary embodiment of the present
invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
Reference will now be made in detail to the preferred embodiments,
examples of which are illustrated in the accompanying drawings.
FIG. 5 is a schematic cross-sectional view showing a passive matrix
organic electroluminescent display device according to an exemplary
embodiment of the present invention.
In FIG. 5, a first electrode 146 is formed on a substrate 110
having a pixel region "P" and a non-pixel region "NP" surrounding
the pixel region "P." The first electrode corresponds to the pixel
region "P." A bank layer 148 having an open portion 149 exposing
the first electrode 146 is formed on the first electrode 146 and
the substrate 110. The bank layer 148 corresponds to the non-pixel
region "NP" and covers edge portions of the first electrode 146.
Further, an organic luminescent layer 150 is formed on the first
electrode 146 in the open portion 149. Accordingly, the adjacent
organic luminescent layers 150 of the adjacent pixel regions "P"
are separated from each other. A second electrode 152 is formed on
the organic luminescent layer 150 and the bank layer 148.
Since the organic electroluminescent (EL) display device has a
passive matrix type, an additional switching element such as a thin
film transistor (TFT) is not formed in the organic EL display
device. In addition, when the first electrode 146 is formed to be
transparent, light generated in the organic luminescent layer 150
is emitted through the first electrode 146 and the organic EL
display device may be referred to as a bottom emission type. For
example, the first electrode 146 may be formed to be transparent by
using a transparent conductive material such as indium-tin-oxide
(ITO) and indium-zinc-oxide (IZO) or by depositing a metallic
material too thin to be transparent.
In this embodiment, the bank layer 148 is formed of a
visible-shielding material shielding a visible ray. When the
visible-shielding material having a transmittance lower than about
10% for visible ray having a wavelength within a range of about 380
nm to about 780 nm is used for the bank layer 148, ambient light
toward the second electrode 152 may be shielded by the bank layer
148. Accordingly, most of reflection of the ambient light from the
second electrode 152 may be prevented and reduction of contrast
ratio is prevented. A light transmittance may be expressed as an
optical density (OD) defined by the equation OD=-Log(T), where T is
transmittance. Accordingly, a transmittance lower than about 10%
may be expressed as an OD higher than about 1.
FIG. 6 is a schematic cross-sectional view showing an active matrix
organic electroluminescent display device according to another
exemplary embodiment of the present invention.
In FIG. 6, an organic electroluminescent (EL) diode "E" is formed
on an array layer "AL." The organic EL diode "E" includes a first
electrode 246, an organic luminescent layer 250 and a second
electrode 252, and the array layer "AL" includes a thin film
transistor (TFT) "T," a storage capacitor "C.sub.ST" and a
plurality of signal lines (not shown). For example, a plurality of
gate lines and a plurality of data lines may be formed as the array
layer "AL." The TFT "T" includes a semiconductor layer 214, a gate
electrode 220 over an active region "Sa" of the semiconductor layer
214, a drain electrode 236 connected to a drain region "Sc" of the
semiconductor layer 214 and a source electrode 238 connected to a
source region "Sb" of the semiconductor region "Sb." A protection
layer 254 is formed on the organic EL diode "E" to protect the
second electrode 252 of the organic EL diode "E." A bank layer 248
having an open portion 249 is formed on the first electrode 246.
The bank layer 248 covers edge portions of the first electrode 246
and the open portion 249 exposes the first electrode 246.
When the second electrode 252 is formed to be transparent, light
generated in the organic luminescent layer 250 is emitted through
the second electrode 252 and the organic EL display device may be
referred to as a top emission type. In this embodiment, the bank
layer 248 is formed of a visible-shielding material shielding a
visible ray. When the visible-shielding material having a
transmittance lower than about 10% for visible ray having a
wavelength within a range of about 380 nm to about 780 nm is used
for the bank layer 248, ambient light toward the TFT "T," the
storage capacitor "C.sub.ST" and the plurality of signal lines may
be shielded by the bank layer 248. Accordingly, most of reflection
of the ambient light from the TFT "T," the storage capacitor
"C.sub.ST" and the plurality of signal lines may be prevented and
reduction of contrast ratio is prevented.
FIGS. 7A to 7C are schematic cross-sectional views showing a
fabricating process of an organic electroluminescent display device
of FIG. 6.
In FIG. 7A, a buffer layer 212 is formed on a substrate 210. A
semiconductor layer 214 of polycrystalline silicon and a first
capacitor electrode 216 are formed on the buffer layer 212 through
a first mask process. The polycrystalline silicon may be obtained
by crystallizing amorphous silicon using a laser or a heat. Next,
the first capacitor electrode 216 is doped with impurities through
a second mask process. A gate insulating layer 218 is formed on the
semiconductor pattern 214 and the first capacitor electrode 216.
Next, a gate electrode 220 and a second capacitor electrode 224 are
formed on the gate insulating layer 218 through a third mask
process. The gate electrode 220 and the second capacitor electrode
224 correspond to a central portion of the semiconductor pattern
214 and the first capacitor electrode 216, respectively. Then, the
semiconductor layer 214 is doped with impurities using the gate
electrode 220 as a doping mask. Since the gate electrode 214
shields the central portion of the semiconductor layer 214, side
portions of the semiconductor layer 214 are doped with impurities
and the central portion of the semiconductor layer 214 remains
intrinsic. After the doping step, the semiconductor layer 214
includes an active region "Sa" corresponding to the gate electrode
220, and a source and a drain regions "Sb" and "Sc" at both sides
of the active region "Sa." After an activation step for the doped
impurities, an interlayer insulating layer 228 is formed on the
gate electrode 220 and the second capacitor electrode 224. The
first and second capacitor electrodes 216 and 224 constitute a
storage capacitor "C.sub.ST" with the gate insulating layer 218
interposed between the first and second capacitor electrodes 216
and 224.
Next, the interlayer insulating layer 228 and the gate insulating
layer 218 are etched through a fourth mask process. Accordingly, a
first contact hole 230 exposing the drain region "Sc" and a second
contact hole 232 exposing the source region "Sb" are formed in the
interlayer insulating layer 228 and the gate insulating layer 218,
and a third contact hole 234 exposing the second capacitor
electrode 224 is formed in the interlayer insulating layer 228.
Next, a drain electrode 236 and a source electrode 238 are formed
on the interlayer insulating layer 228 through a fifth mask
process. The drain electrode 236 is connected to the drain region
"Sc" through the first contact hole 230. In addition, the source
electrode 238 is connected to the source region "Sb" through the
second contact hole 232 and is connected to the second capacitor
electrode 224 through the third contact hole 234. The semiconductor
layer 214, the gate electrode 220, the drain electrode 236 and the
source electrode 238 constitute a thin film transistor "T." Then, a
passivation layer 242 is formed on the drain electrode 236 and the
source electrode 238. Next, the passivation layer 242 is etched
through a sixth mask process to form a drain contact hole 244
exposing the drain electrode 236. Next, a first electrode 246 is
formed on the passivation layer 242 through a seventh mask process.
The first electrode 246 is connected to the drain electrode 236
through the drain contact hole 244. Although not shown in FIG. 7A,
the first electrode 246 of one pixel region is separated from an
adjacent first electrode in another pixel region.
In FIG. 7B, a bank layer 248 is formed on the passivation layer 242
through an eighth mask process. The bank layer 248 covers edge
portions of the first electrode 246, and has an open portion
exposing the first electrode 246. In addition, the bank layer 248
is formed of a visible-shielding material shielding a visible ray.
When the visible-shielding material having a transmittance lower
than about 10% for visible ray having a wavelength within a range
of about 380 nm to about 780 nm is used for the bank layer 248,
ambient light toward the TFT "T," the storage capacitor "C.sub.ST"
and the plurality of signal lines may be shielded by the bank layer
248. Accordingly, most of reflection of the ambient light from the
TFT "T," the storage capacitor "C.sub.ST" and the plurality of
signal lines may be prevented and reduction of contrast ratio is
prevented.
In FIG. 7C, an organic luminescent layer 250 and a second electrode
252 are sequentially formed on the first electrode 246 and the bank
layer 248. Then, a protection layer 254 is formed on the second
electrode 252.
FIGS. 8 and 9 are schematic cross-sectional views showing an active
matrix organic electroluminescent display device according to
another exemplary embodiment of the present invention. FIG. 8 shows
a portion of the active matrix organic electroluminescent display
(AMOELD) device corresponding to one pixel region, while FIG. 9
shows a whole AMOELD device.
In FIGS. 8 and 9, an array layer "AL" including a thin film
transistor "TFT," a storage capacitor "C.sub.ST" and a plurality of
signal lines (not shown) such as gate lines and data lines is
formed on a substrate 310 having a pixel region "P" and a non-pixel
region "NP," and an organic electroluminescent (EL) diode "E"
including a first electrode 346, an organic luminescent layer 350
and a second electrode 352 is formed on the array layer "AL." The
non-pixel region "NP" surrounding the pixel region "P" represents a
portion where light is not emitted and which is not used for
displaying images. For example, the non-pixel region "NP"
corresponds to an area between the adjacent first electrodes 346.
An encapsulation substrate 370 is disposed to face and be spaced
apart from the organic EL diode "E." A black matrix 372
corresponding to the non-pixel region "NP" is formed on an inner
surface of the encapsulation substrate 370.
When the second electrode 352 is formed to be transparent and,
light generated in the organic luminescent layer 350 is emitted
through the second electrode 352 and the organic EL display device
may be referred to as a top emission type. In this embodiment, the
black matrix 372 is formed of a visible-shielding material
shielding a visible ray and the encapsulation substrate 370 is
formed of a transparent material. When the visible-shielding
material having a transmittance lower than about 10% for visible
ray having a wavelength within a range of about 380 nm to about 780
nm is used for the black matrix 372, ambient light toward the TFT
"T," the storage capacitor "C.sub.ST" and the plurality of signal
lines may be shielded by the black matrix 372. Moreover, since the
black matrix 372 covers the second electrode 352 in the non-pixel
region "NP," ambient light toward the second electrode 352 in the
non-pixel region "NP" may be shielded by the black matrix 372.
Accordingly, most of reflection of the ambient light from the TFT
"T," the storage capacitor "C.sub.ST," the plurality of signal
lines and the second electrode 352 may be prevented and reduction
of contrast ratio is prevented.
Even though the organic EL display device of FIGS. 8 and 9 has an
active matrix type including a switching element such as the TFT
"T," an encapsulation substrate having a black matrix may be used
for a passive matrix organic EL display device in another
embodiment.
FIG. 10 is a schematic cross-sectional view showing an organic
electroluminescent display device according to another embodiment
of the present invention.
In FIG. 10, an array layer "AL" is formed on a substrate 410 having
a pixel region "P" and a non-pixel region "NP," and an organic
electroluminescent (EL) diode "E" including a first electrode 446,
an organic luminescent layer 450 and a second electrode 452 is
formed on the array layer "AL." The first electrode 416 corresponds
to the pixel region "P." A bank layer 448 is formed between the
array layer "AL" and the second electrode 448. The bank layer 448
corresponds to the non-pixel region "NP" and may cover edge
portions of the first electrode 446. In addition, an encapsulation
substrate 470 is disposed to face and be spaced apart from the
second electrode 452.
When the first electrode 446 is formed to be transparent and the
encapsulation substrate 470 is formed of an opaque material, light
generated in the organic luminescent layer 450 is emitted through
the first electrode 446 and the organic EL display device may be
referred to as a bottom emission type. In this embodiment, the bank
layer 448 is formed of a visible-shielding material shielding a
visible ray. When the visible-shielding material having a
transmittance lower than about 10% for visible ray having a
wavelength within a range of about 380 nm to about 780 nm is used
for the bank layer 448, ambient light toward the second electrode
452 may be shielded by the bank layer 448. Accordingly, most of
reflection of the ambient light from the second electrode 452 may
be prevented and reduction of contrast ratio is prevented.
Even though the organic EL display device of FIG. 10 has an active
matrix type including a switching element such as the thin film
transistor (TFT), an encapsulation substrate of an opaque material
and a back layer of a visible-shielding material may be used for a
passive matrix organic EL display device in another embodiment.
FIGS. 11A and 11B are schematic cross-sectional views showing a
fabricating process of an organic electroluminescent (EL) display
device according to another exemplary embodiment of the present
invention.
In FIG. 11A, a thin film transistor (TFT) "T" including a
semiconductor layer 514, a gate electrode 520, a drain electrode
536 and a source electrode 538 and a storage capacitor "C.sub.ST"
including a first electrode 516 and a second electrode 524 are
formed on a substrate 510. After a first electrode 546 connected to
the drain electrode 536 is formed on a passivation layer 542, a
bank layer 548 is formed on the passivation layer 542. The bank
layer covers edge portions of the first electrode 546 and has an
open portion 549 exposing the first electrode 546.
In addition, the bank layer 548 is formed of a UV-shielding
material shielding an ultra violet (UV) ray. The UV-shielding
material may have a transmittance lower than about 3% for UV ray
having a wavelength within a range of about 150 nm to about 300 nm.
In other words, the UV-shielding material may have an optical
density (OD) higher than about 1.5 for UV ray corresponding to a
range of about 150 nm to about 300 nm. For example, the
UV-shielding material may include an organic insulating material
such as polyimid (PI), benzocyclobutene (BCB) and acrylic resin.
Further, the bank layer 548 may be formed to have a thickness
greater than about 1 micrometer.
After the bank layer 548 is formed, a cleaning step using a UV ray
is performed for removing particles from the second electrode 546.
Since the bank layer 548 is formed of a UV-shield material, the UV
ray toward the semiconductor layer 514 is shielded during the
cleaning step by the bank layer 548. Accordingly, deterioration of
the TFT in characteristics is prevented.
In FIG. 11B, after the cleaning step, an organic luminescent layer
550 and a second electrode 552 are sequentially formed on the first
electrode 546 to constitute an organic EL diode "E." A protection
layer 554 is formed on the second electrode 552.
In an organic EL display device according to another exemplary
embodiment of the present invention, a bank layer may be formed of
a light-shielding material shielding visible ray and UV ray. For
example, the light-shielding material may have a transmittance
lower than about 3% for UV ray having a wavelength within a range
of about 150 nm to about 300 nm and lower than about 10% for
visible ray having a wavelength within a range of about 380 nm to
about 780 nm. Accordingly, deterioration of the TFT in
characteristics due to UV ray is prevented and reduction of
contrast ratio of the organic EL display device due to reflection
of ambient light is prevented.
In the present invention, reduction of contrast ratio of an organic
EL display device is prevented by using a bank layer of a material
shielding visible ray or by using a black matrix on an
encapsulation substrate. Furthermore, deterioration of a TFT in
characteristics is prevented by using a bank layer of a material
shielding UV ray. Therefore, display quality of the organic EL
display device is improved.
It will be apparent to those skilled in the art that various
modifications and variations can be made in the organic
electroluminescent display device and the method of fabricating the
same of the present invention without departing from the sprit or
scope of the invention. Thus, it is intended that the present
invention covers the modifications and variations of this invention
provided they come within the scope of the appended claims and
their equivalents.
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